The invention relates to computer systems with cooling subsystems for cooling of heat producing elements within the computer. More particularly, the invention relates to fan cooling subsystems as used in many personal computers today. Even more particularly, the invention relates to fan cooling subsystems for personal computer systems wherein the speed of the fan is adjusted based on the temperature within the personal computer system housing.
Many computer systems today, and nearly all desktop personal computers, use a fan cooling subsystem to cool off the heat producing elements within the computer. These fans are generally situated in an opening in the computer housing, and may direct air into or out of the housing. In most computer systems, the fan blows at a constant speed.
A very rapidly spinning fan exchanges the air in the box quickly, so when the load inside a computer is producing a lot of heat, its fan needs to spin very rapidly, but when the load elements are producing only a little heat, the fan may spin more slowly.
A rapidly spinning fan makes considerably more noise than a slowly spinning fan. Thus, there is a trade off between the speed with which heat may be dissipated by a fan and the noise produced by the fan. Therefore, some computer makers have found it desirable to provide two speeds for their fans. When the computer's elements are operating at a low temperature, the fan blows quietly at a low speed. When the computer's elements are hot, however, the system blows rapidly and loudly. Thus, sound quality is sacrificed only when high temperatures make a high fan speed necessary.
The two-speed fan subsystem has certain problems. When the temperature inside the computer is at an intermediate level, the slow speed of the fan cannot cool the system, and the high speed of the fan is unnecessarily loud. Thus, the two-speed fan subsystem proves inefficient in such circumstances. A three-speed fan subsystem would provide an intermediate fan speed, but would unnecessarily complicate the fan control circuitry.
Thus, there is a need for a fan subsystem which can increase the fan speed proportionally to the increase in the temperature of the computer's elements. Such a fan subsystem would evenly match the temperature inside the computer with the fan speed necessary to cool the system. Thus, a computer system with such a fan subsystem would provide the most efficient trade off between fan speed and sound quality.
Additionally, if the temperature inside the computer gets too hot, then the fan may not be able to cool the system even at the high speed of a two-speed fan subsystem. In this case, the computer system will overheat and possibly damage some of the computer's elements. Likewise, if the fan is missing or becomes blocked and unable to spin, then there will be no airflow to the heat producing elements, so the system may overheat in this situation, too. Therefore, there is a need for a fan subsystem with control circuitry which can protect against overheating due to inadequate fan speed, a missing fan, or a blocked fan.